This invention relates to grinding and polishing of preforms for optical lenses and, more particularly, to performing these operations simultaneously.
The use of high-speed, air-bearing spindles in grinding operations is known. The optimization of speed, stiffness, rotational accuracy, and vibrationless operation can produce surfaces on many materials with roughness values in the fractional microinch range and surface figures of a fraction of a wave. These good results are generally obtained by single-point cutting of plastics and soft metals. See, for example, Donaldson, R. R., Patterson, S. R. and Thompson, D. C., "Diamond-Machining and Mechanical Inspection of Optical Components" UCRL-86897, Lawrence Livermore National Laboratory, Livermore, CCA, Nov. 13, 1981; and Brehm, P. D., "Making the Most of Precision Machining", Photonics Spectra, June 1982.
Precision glass optical elements may be formed in molds having a precise configuration. U.S. Pat. No. 4,481,023-Marechal and Maschmeyer decribes the molding of a glass lens having dimensional tolerances finer than 0.1% and surface figure tolerances finer than 0.2 .lambda./cm in the visible range of the radiation spectrum.
The molding of aspheric lenses in accordance with the Marechal and Maschmeyer patent requires that a precise preform, or blank, be produced with two polished surfaces. These precise preforms are then pressed in a mold to the final finished form. For example, for small lenses for audio and video players, the preform shape is a bi-convex lens of about 7-14 millimeter diameter. The current process for producing the preform for such lenses uses a grinding process to produce the shape of the preform. Then, conventional lapping and polishing steps produce the required finish on the lens preform.
It is an object of the present invention to produce a ground and polished optical surface on a glass lens preform in a single operation.
It is a further object of the present invention to produce spherical, prolate, and other complex optical surfaces by a grinding and polishing operation.